JPH06281947A - Liquid crystal panel and its production - Google Patents

Abstract

PURPOSE:To expand the visual angle of the liquid crystal panel and to obtain a good display grade by subjecting one of the substrates of the liquid crystal panel to an orientation treatment. CONSTITUTION:The liquid crystal panel 11 is formed out of liquid crystal unit cells 13 segmented by level differences or wall surfaces 12 smaller than one pixel. The one unit cell has internally a pretilt angle of nearly 0 deg. to a liquid crystal molecule 15 at nearly the center with respect to the cell thickness of the liquid crystal layer 14 when an electric field is not impressed. The pretilt angle of the liquid crystal molecule at the center is nearly 0 deg. and, therefore, the direction inclining with the electric field is not regulated and may incline in any directions at the time of impressing the electric field. As the result, liquid crystal regions 16 (domains) inclined in the directions different from each other eventually coexist within the one pixel. The respective domains are larger than the one pixel if there are no wall surfaces 12 segmenting the respective liquid crystal unit cells, but if the cells are segmented by the wall surfaces 12, the growth of the domains is stopped in this range and the visual angle is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front panel, and more particularly to a liquid crystal panel and its manufacturing method.

[0002]

2. Description of the Related Art Conventionally, the following methods have been used to expand the viewing angle of a liquid crystal panel. (1) Light leaks due to a change in the viewing angle due to a change in the geometrical transmission axis of the polarizing plate itself.

In order to prevent this, a retardation plate is inserted between the polarizing plate and the liquid crystal panel. As a reference March 1992
Organized by the Society of Polymer Science, Polymer Possibility Lecture "Liquid Crystal Display Beyond CRT" Lecture Collection Page 43. (2) An optical compensation method using a retardation plate having a negative refractive index. (For reference, Yamauchi et al.
89 digest, 378 pages, 1989: S. Yama
uchi, et.al., SID 89 DIGEST, p.378 (1989)). (3) The viewing angle dependence of the liquid crystal molecules with respect to the electric field is reduced by dividing the unit picture element into domains with different tilts to reduce the viewing angle dependence of the liquid crystal panel as a whole. The following are detailed as references.

A) K.Y.Yan "Two Main Twisted Nematic Ant Tilted Homeotropic Liquid Kit Crystal Display for Active Matrix Application" Id Earl 91 91w Twisted (1991): Twisted (1991): KHYANG
nd Tilted Homeotoropic Liquid Crystal Display for A
ctive Matrix Applications ", IDRC DIGEST, p.68 (1991) b) Koike et al., SAI Day 92 Digest, 79
Page 8 (1992): Y.Koike et.al., SID 92 DIGEST
p.798 (1992) c) Takatori et al., IDR 92 digest, page 591 (1992): K. Takatori et.al.,
IDRC 92 DIGEST, p.591 (1992) (4) The viewing angle is enlarged by using a random alignment by using a polymer-liquid crystal complex. The following are detailed as references.

Etch. Yoshida et al.
92 Digest, page 631 (1992): H.Yo
shida et.al., IDRC 92 DIGEST, p.631 (1992)

[0006]

However, there are the following problems with respect to the above conventional techniques. (1) The method using a retardation plate or a retardation plate having a negative refractive index ((1) and (2) above) cannot compensate the viewing angle dependence when liquid crystal molecules are tilted by an electric field. (2) The method of dividing the picture element ((3) above) requires the use of a photo process, which complicates the process. (3) In the case of using random alignment ((4) above), if a polarizing plate is used, the light utilization efficiency is deteriorated because the alignment treatment is not performed, resulting in darkness.

[0007]

In view of the above problems, in the present invention, one picture element is divided by a wall surface, and a tilt angle of a liquid crystal molecule corresponding to a central portion of a liquid crystal layer when no electric field is applied (hereinafter referred to as a pretilt angle of a midplane). : Θp (m))) is set to almost 0 degree, so that the viewing angle characteristics can be improved by inducing a large number of domains in which liquid crystal molecules have different tilt directions when an electric field is applied.

[0008]

The operation of the present invention will be described below with reference to the drawings.

1A and 1B are schematic sectional views of a liquid crystal panel showing the operation of the present invention. The liquid crystal panel 11 is composed of liquid crystal unit cells 13 which are smaller than one picture element and are separated by a step or a wall surface 12.

When there is no electric field in one unit cell (FIG. 1 (a)), the liquid crystal molecule 15 at the center of the cell thickness of the liquid crystal layer 14 has a pretilt angle (θp (m)) of about 0 degrees. ing.

When an electric field is applied (FIG. 1 (b)), since θp (m) of the central liquid crystal molecule is almost 0 degree, the direction inclining to the electric field is not regulated, and either direction is inclined. Is also good.

Therefore, as a result, liquid crystal regions 16 (hereinafter referred to as domains) tilted in different directions as shown in FIG. 1B are mixed in one picture element.

At this time, if there is no wall surface that divides each liquid crystal unit cell, each domain becomes larger than one picture element, and a portion having a different viewing angle becomes noticeable.

If separated by the wall surface, the growth of the domain can be stopped within that range, and the viewing angle can be improved.

[0015]

【Example】

(Embodiment 1) FIG. 2 shows a configuration diagram of a general TFT liquid crystal panel which is an embodiment.

FIG. 2 (a) is a plan view showing the structure of a liquid crystal element in which a TFT element is formed on one substrate, and FIG. 2 (b).
Shows a cross-sectional view taken along the line AA ′ in FIG.

A pixel electrode 21 formed of an ITO film is formed on one glass substrate 25a, and a gate electrode 23 is formed around the pixel electrode 21.
And source electrodes 22 are arranged in a matrix. The source electrode 22 is formed about 500 nm higher than the pixel electrode 21.

Between the source electrode 22 and the pixel electrode 21, a switching operation is performed by a gate pulse.
The FT element 24 is formed. On the other substrate 25b, an ITO film to be the counter electrode 26 is formed.

An embodiment of the present invention will be described below. The size of the pixel electrode 21 was 350 × 350 μm. A method of forming a step in a unit smaller than the pixel electrode on the ITO film of the counter substrate will be described below.

Negative photoresist ON on ITO substrate
NR-20 (manufactured by Tokyo Ohka Co., Ltd.) is applied by a spinner, prebaked, and subjected to a normal process using a photomask (according to the catalog of Tokyo Ohka Co., Ltd.), followed by the simplification of FIG. As shown in the figure, one picture element was divided into four with a lattice-like step having a thickness of about 2.5 μm. In FIG. 3, 32 is the size of one picture element,
Reference numeral 31 is a grid-like step, 31 is a substrate, and 34 is a cut for facilitating the injection of liquid crystal. The liquid crystal was difficult to inject in the closed loop structure without breaks.

First, a polyimide alignment film Optomer AL-2061 manufactured by Japan Synthetic Rubber Co., Ltd. was applied by a printing method on each of the substrates with a TFT element and with a lattice-shaped step. The curing temperature was 190 ° C. for 30 minutes in a clean oven. The polyimide film thickness was about 60 nm.

Next, both substrates were subjected to rubbing treatment with rayon cloth so as to form a counterclockwise splay-aligned TN cell (see FIG. 4: 41 in FIG. 4 is the rubbing direction of the upper substrate, and 42 is the lower direction). The rubbing direction of the substrate).

By performing the rubbing process in this manner, the pretilt angles on the upper and lower substrates were in the same direction, and the splay orientation was obtained, and θp (m) could be set to almost 0 degree.

A sealing portion was formed on the counter substrate by screen-printing an epoxy adhesive, and then Micropearl (produced by Sekisui Fine Chemical Co., Ltd. (average particle size: 5) was used.
μm) was evenly sprayed.

The counter substrate that has been subjected to the above-mentioned processing and TF
Approximately 1kg after pasting with one substrate with T element
While uniformly pressurizing at a pressure of / cm2, it was heated and cured at 150 ° C for 1 hour to prepare an empty cell having a counterclockwise TN orientation.

A liquid crystal material prepared by mixing liquid crystal ZLI4792 manufactured by Merck Ltd. with a chiral agent S811 manufactured by Merck Ltd. at a pitch of 80 μm was injected into the cell manufactured as described above by a vacuum injection method. did. After the injection was completed, the injection port was sealed with an epoxy sealant. The liquid crystal had no bubbles because of the break, and could be uniformly filled.

TN with TFT element manufactured in this way
In the liquid crystal panel, a gate pulse is applied to the gate electrode and an operation signal voltage is applied to the source electrode to perform active matrix driving. The operation signal voltage was driven by driving in which adjacent source electrodes have the same polarity and the polarity is inverted every field (one-field inversion drive).

In addition, the polarizing plates were arranged in a crossed Nicol display. Looking at the driven display, the viewing angle was wide and the quality was good.

Further, it was confirmed that the liquid crystal molecules were tilted in different directions in each of the four divided unit cells by observing the image with a magnifying glass while changing the viewing angle direction.

As a comparative example, even when the ITO substrate, which is the counter electrode, is not provided with the grid-like steps, when a panel is produced and driven in the same manner as described above, the domain becomes larger than one pixel. The parts with different viewing angle characteristics were noticeable, and the display quality was impaired.

(Embodiment 2) A TF having the same structure as that of Embodiment 1.
A substrate with a T element and a counter substrate with a step were produced. The alignment film is a monobasic chromium complex for vertical alignment (for the manufacturing method, refer to References Matsumoto et al. Applied Physics Letters Vol. 27, p. 268 (1975): S. Matsumoto.
See et.al., Appl. Phys. Lett., 27, p.268 (1975). ) Was used according to the above reference.

The liquid crystal material is MJ90 manufactured by Merck Japan Ltd.
2880 was used. The cell thickness was 4.5 μm.

The other manufacturing method was carried out according to Example 1. When driven and displayed in the same manner as in Example 1, the viewing angle was wide and the display was good. Further, when magnified with a loupe and observed while changing the viewing angle direction, it was confirmed that the liquid crystal molecules were tilted in different directions in each of the four divided unit cells.

Example 3 A polymer composite type liquid crystal panel which is an example of the present invention will be described below with reference to the drawings.

TF having an alignment film or the like as in Example 1
A substrate with a T element and a counter ITO substrate were produced and assembled as a panel in the same manner as in Example 1.

The orientation treatment was individually performed in the same manner as in Example 1 so that θp (m) became approximately 0 degrees.

The UV curable monomer (INC 90: manufactured by Nippon Kayaku Co., Ltd.) and the nematic liquid crystal used in Example 1 were 1: 1.
The mixture having the weight ratio of 0 was poured in the same manner as in Example 1 and the hole was sealed.

Further, the same chiral agent as in Example 1 was added to the nematic liquid crystal and left counterclockwise.

Thereafter, as shown in FIG. 5, UV irradiation is first performed at 30 ° C. and an ultraviolet intensity of 200 mW / using a lattice-shaped mask 51 divided into small units 53 each having a size of 1/4 of one picture element 52.
Irradiation at cm2 for 1 minute. After being partially cured in this way, the UV intensity is 200 mW over the entire display area at a temperature of 30 ° C.
It was cured by irradiating it with ultraviolet rays for 1 minute at / cm 2.

Further, when the completed liquid crystal panel was observed, the liquid crystal unit cells were divided to some extent along the grid.

When display driving was performed in the same manner as in Example 1, good viewing angle characteristics were exhibited. Further, even if the liquid crystal unit cells are not intentionally separated using the mask as described above, the liquid crystal is divided into a fine network structure by the polymer, and therefore the polymer dispersed liquid crystal is effective in expanding the viewing angle.

Further, in this example, although it was a composite with a polymer, since it was subjected to an alignment treatment, it did not become dark even if a polarizing plate was used, and a brightness almost equal to that of a normal TN was obtained.

[0043]

The present invention expands the viewing angle of a liquid crystal panel,
A liquid crystal panel having a good display quality can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a liquid crystal panel showing the operation of the present invention.

FIG. 2 is a configuration diagram of a general TFT element in an example.

FIG. 3 is a simplified diagram of a stepped substrate according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a rubbing treatment method for spray alignment according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of a lattice-shaped photomask used in an example of the present invention.

[Explanation of symbols]

 11 liquid crystal panel 12 one picture element 13 liquid crystal unit cell 14 liquid crystal layer 15 central liquid crystal molecule 16 liquid crystal region (domain)

Claims (10)

[Claims] 1. A liquid crystal unit cell, which is smaller than one picture element divided by a step or a wall surface, has at least one polarizing plate, and at least one of substrates of a liquid crystal panel is subjected to an alignment treatment. LCD panel characterized by. 2. The liquid crystal panel according to claim 1, wherein the liquid crystal molecules are tilted in different directions at least between the liquid crystal unit cells when an electric field is applied. 3. The liquid crystal panel according to claim 1, wherein the step or the wall surface has a shape that does not form a closed loop. 4. The liquid crystal panel according to claim 1, 2 or 3, wherein the liquid crystal panel is a twisted nematic liquid crystal panel. 5. The liquid crystal panel according to claim 1, 2 or 3, wherein the liquid crystal panel uses a homeotropic nematic system. 6. The liquid crystal panel according to claim 1, wherein the tilt of the molecule corresponding to the central portion of the liquid crystal layer of the liquid crystal panel with respect to the cell thickness direction is approximately 0 degrees in the absence of an electric field. 7. A liquid crystal panel according to claim 1, comprising a composite of a polymer and a liquid crystal. 8. The liquid crystal panel according to claim 7, wherein the liquid crystal panel is manufactured by including at least a process of partially curing a mixture of liquid crystal and a polymer precursor. 9. The liquid crystal panel according to claim 8, wherein the means for partially curing is ultraviolet curing. 10. A method of manufacturing a liquid crystal panel according to claim 8 or 9.